1. Field of the Invention
The present invention relates to a noise injection apparatus for injecting noise to a printed circuit board that is used for noise analysis of the printed circuit board.
2. Description of the Related Art
In order to process huge amounts of information, techniques are being developed for increasing the operation speed of electronic devices, and in turn, EMI (Electromagnetic Interference) discharged from the electronic device is increasing so that countering such noise is becoming difficult. It is noted that EMI radiated from an electronic device may cause operation errors of neighboring electronic devices. Thus, many countries impose certain EMI legal requirements, and in such countries, import and distribution of electronic devices may not be authorized unless the electronic devices conform to the EMI requirements. When electronic devices fail to satisfy EMI requirements, the distribution and sales of the electronic devices may have to be stopped so that the company responsible for distributing the electronic devices may suffer significant damages. Despite such a risk of damage, countermeasures against EMI have not been taken into serious consideration in the field of electronic device technology.
It is noted that the number of noise sources in a printed circuit board has increased due to increased operation speed, complication in design, and high densification of the circuit, and in turn, determination of the noise source is becoming difficult. Of particular concern is noise emitted from a device IC due to increased circuit operation speed.
However, since a number of noise sources exist within a printed circuit board, it is quite difficult to determine the noise source that is generating noise at a problematic frequency.
If there were only one noise source, noise generated within the printed circuit board at a predetermined frequency may be easily measured using a commercial noise visualization apparatus, for example, to determine whether a problem exists and find the cause of the problem based on the noise distribution analysis obtained by the noise visualization apparatus.
It is noted that a method of injecting noise to a printed circuit board is disclosed in Japanese Patent No. 3263672 (“Apparatus and Method for Injection of Noise”), for example. Specifically, the above reference discloses a technique that involves superposing noise (common mode or normal mode) on a commercial power supply while the power of a measured device is turned on, and injecting noise (common mode or normal mode) to the power supply and ground of the measured device. However, according to this method, since noise is injected into the power supply of a unit, the noise source that is causing a problem may not be identified.
Also, since emissions from a device (IC) may be in various frequency bands, noise has to be injected while taking into account the impedance of the noise injecting unit according to the frequency band of the noise being injected.
Further, the disclosed method is limited to assessing noise of a device in operation. However, it is desired that noise evaluation be made possible at the substrate level before the device may be fully operated to determine how noise radiates from the power supply, for example.
It is noted that another related technique is disclosed in Japanese Laid-Open Patent Publication No. 2002-318253 (“Noise Visualization System and Display Method thereof”), for example. Specifically, the above reference discloses a method of injecting a high frequency signal that simulates noise to an examined object from an injection probe via a wire harness. However, in the above-disclosed technique, standing wave that may be superposed on a cable that connects a signal generator to the probe is not taken into consideration, and measurement results obtained from the noise visualization system according to the disclosed technique may be affected by the emissions from the cable. Thus, the actual noise measurements of the substrate itself may not be obtained using this technique.
Also, if measurement results of the substrate itself cannot be obtained by the noise visualization system due to emissions from the cable, this means that measurement results may vary depending on the positional relation between the cable and the substrate at the time of measurement. Therefore, a measurement method is desired that can block interference by the emissions from the cable.
It is noted that another related technique is disclosed in Japanese Utility Model Publication No. 62-8534 (“Noise Simulator”), for example. Specifically, the above reference discloses a technique that involves applying a pulse voltage from a pulse generating circuit via a coupler to a circuit component of an examined device such as one of a group of ICs mounted on a printed circuit board. In this way, a pulse voltage may be applied to each individual IC to identify the IC that is causing the same operation error as the operation error that is currently occurring in the device and implement countermeasures for the relevant IC and associated circuits thereof. However, according to this technique, the coupler is merely a flat metal plate or a metal plate arranged into a horse shoe shape that is coated with insulating material, and a matching device is not used so that efficient application of noise may be difficult.
As can be appreciated, plural noise sources exist within a printed circuit board, and identifying the noise source generating noise at the problematic frequency has been quite difficult. In the case where a method of injecting noise into the power supply of a unit is employed, the noise source causing a problem within the unit cannot be identified.
Also, in the case of implementing the technique disclosed in Japanese Patent No. 3263672, since emissions from a device (IC) may be in various frequency bands, noise has to be injected while taking into account the impedance of the noise injection unit according to the frequency band of the noise being injected.
Further, the above technique is limited to implementation for a device that is in operation. However, it is desired that noise evaluation be enabled to determine how noise is radiated from the power supply, for example, at the substrate level or before the device can be fully operated.
In the case of implementing the technique disclosed in Japanese Laid-Open Patent Publication No. 2002-318253, emissions from the cable may be included in the measurement results obtained by the noise visualization system so that the actual noise measurement of the substrate itself may not be obtained. When noise measurement of the substrate itself cannot be obtained due to emissions from the cable, measurement results may vary depending on the positional relation between the cable and the substrate.
In the case of implementing the technique disclosed in Japanese Utility Model Publication No. 62-8534, a flat metal plate or a metal plate arranged into a horse shoe shape that is coated by an insulating material has to be used as the coupler. Although, emissions from a coaxial cable may be prevented by such an arrangement, noise may not be efficiently transmitted in this case and deviations may occur in measurements so that accurate measurement may not be obtained.
Also, it is noted that the above disclosures are concerned with noise coming into a device; however, there is a need to consider noise being emitted out of a device as well.